A conventional data storage system typically includes an array of disk drives and a storage processor (or a storage director). During operation, the storage processor stores data onto and retrieves data from the array of disk drives on behalf of one or more external host devices.
It is common for the data storage system to store data in compliance with a particular RAID (redundant array of inexpensive disks) level, e.g., RAID level 0 (disk mirroring), RAID level 5 (striped data and parity), etc. For example, the conventional data storage system may include three disk drives A1, A2, and A3, which are configured as a first RAID group running RAID level 5 and which are installed in enclosure slots S1, S2, and S3, respectively. The conventional data storage system may further include three other disk drives B1, B2, and B3, which are configured as a second RAID group running RAID level 5 and which are installed in enclosure slots S4, S5, and S6, respectively. In the above-described conventional data storage system, the data on a particular disk drive of a RAID group is capable of being recovered if that particular disk drive fails. For example, suppose that disk drive A2 of the first RAID group fails and that the conventional data storage system notifies a system administrator. Further suppose that the system administrator responds to the failure by removing disk drive A2 from slot S2 and installing a replacement disk drive R into slot S2.
Upon installation of replacement disk drive R into slot S2, the conventional data storage system checks whether there is RAID group information on replacement disk drive R to see whether replacement disk drive R is disk drive A2. Since the RAID group information on replacement disk drive R indicates that the newly installed disk drive within slot S2 is not disk drive A2, the conventional data storage system responds by immediately beginning reconstruction of the data that was stored on disk drive A2 from the remaining data on disk drives A1 and A3, and automatically writing the reconstructed data onto replacement disk drive R in slot S2. In particular, the conventional data storage system saves new RAID group information on replacement disk drive R to indicate that replacement disk drive R now belongs to the first RAID group in place of failed disk drive A2, and then writes the reconstructed data onto replacement disk drive R.
Once this data recovery process is complete, the first RAID group which has now been properly restored (i.e., the first RAID group now includes disk drives A1, R, and A3) is capable of carrying on as before. That is, the conventional data storage system continues with both the first and second RAID groups enjoying normal RAID level 5 operation.